Often termed electron paramagnetic resonance (EPR), which is a more precise terminology when the measured spectra arise from weakly-interacting unpaired electrons, the ESR technique is also applicable to weakly interacting ferro- or ferri-magnetic minerals in small particle sizes. In the latter case, the experiment is called ferromagnetic resonance (FMR) ...even though the spectra are recorded in the exact same way as EPR. The following encyclopedia entry provides a short, but sufficiently technical, review of applications of ESR/EPR to paramagnetic species in crystals and glasses:

The slides below were adapted from work described in publications (2) and (3), which specifically treat the Cretaceous-Tertiary or K-T Boundary (recently changed to Cretaceous-Paleogene or K-Pg Boundary) corresponding to the impact of an asteroid about 66 million years ago that brought about the extinction of the dinosaurs and many other species. The stratigraphic columns studied comprised limestones that were on the sea floor before, during, and after the time of the impact. However, also examined were ejecta clasts and fire-ball accretionary lapilli created by explosive excavation of the 180-to-200 km-diameter crater buried beneath México’s Yucatán Peninsula. See (6) for latest quasi-consensus on the bases for linking this impact to the mass extinction.

About Me

B.S. in Physics, Carnegie-Mellon University, 1960 Ph.D. in Physics, Brown University, 1966. Fellow, American Physical
Society. Fellow, American Association for the Advancement of Science.
Fellow, American Ceramic Society. Member, Geological Society of America, Research Physicist at Naval Research Laboratory (NRL), Washington, DC,
1967-2001. Fulbright-García Robles Fellow at Universidad Nacional
Autónoma de México, 1997. Invited Professor of Research at Universités
de Paris-6 & 7, Lyon-1, et St-Etienne (France) and Tokyo Institute
of Technology, 2000-2004. Adjunct Professor of Materials Science and
Engineering, University of Arizona, 2004-2005. Consultancy: impactGlass
research international, 2005-present.
Winner, one national and two international research awards and honored
by Brown University with a "Distinguished Graduate School Alumnus
Award." Author, 198 papers in peer-reviewed journals and books, Principal Author of 114 of these.